As many of you know when you have two adjacent demes, breeding populations, they often rapidly equilibrate in gene frequencies if they were originally distinct. There are plenty of good concrete examples of this. The Hui of China are Muslims who speak local Chinese dialects. The most probable root of this community goes back to the enormous population of Central Asia Muslims brought by the Mongol Yuan dynasty that ruled ruled China for over a century from the late 1200s to 1300s. Genetic studies of this group that I’ve seen indicate that a high bound estimate for West Eurasian ancestry is ~10%. The other ~90% is interchangeable with the Han Chinese. So let’s assume that the Hui are ~10% West Asian. If you assume that in the year 1400 the Hui were “pure,” you have 24 generations (25 years per generation). The original population of “Central Asian Muslims” were heterogeneous, including Iranians and Turks. But let’s take it granted that they were 50% East Eurasian and 50% West Eurasian in ancestry at the time of their arrival. What would the intermarriage rate per generation have to be so ...
July 7, 2011
June 27, 2011
The image above is adapted from the 2010 paper A Predominantly Neolithic Origin for European Paternal Lineages, and it shows the frequencies of Y chromosomal haplogroup R1b1b2 across Europe. As you can see as you approach the Atlantic the frequency converges upon ~100%. Interestingly the fraction of R1b1b2 is highest among populations such as the Basque and the Welsh. This was taken by some researchers in the late 1990s and early 2000s as evidence that the Welsh adopted a Celtic language, prior to which they spoke a dialect distantly related to Basque. Additionally, the assumption was that the Basques were the ur-Europeans. Descendants of the Paleolithic populations of the continent both biologically and culturally, so that the peculiar aspects of the Basque language were attributed by some to its ancient Stone Age origins.
As indicated by the title the above paper overturned such assumptions, and rather implied that the origin of R1b1b2 haplogroup was in the Near East, and associated with the expansion of Middle Eastern farmers from the eastern Mediterranean toward western Europe ~10,000 years ago. Instead of the high frequency of R1b1b2 being a confident peg for the ...
June 10, 2011
In light of my last post I had to take note when Dienekes today pointed to this new paper in the American Journal of Physical Anthropology, Population history of the Red Sea—genetic exchanges between the Arabian Peninsula and East Africa signaled in the mitochondrial DNA HV1 haplogroup. The authors looked at the relationship of mitochondrial genomes, with a particular emphasis upon Yemen and the Horn of Africa. This sort of genetic data is useful because these mtDNA lineages are passed from mother to daughter to daughter to daughter, and so forth, and are not subject to the confounding effects of recombination. They present the opportunity to generate nice clear trees based on distinct mutational “steps” which define ancestral to descendant relationships. Additionally, using neutral assumptions mtDNA allows one to utilize molecular clock methods to infer the time until the last common ancestor of any two given lineages relatively easily. This is useful when you want to know when a mtDNA haplgroup underwent an expansion at some point in the past (and therefore presumably can serve as a maker for the people who carried those lineages and their past ...
May 4, 2011
A new paper in Proceedings of the Royal Society dovetails with some posts I’ve put up on the peopling of Japan of late. The paper is Bayesian phylogenetic analysis supports an agricultural origin of Japonic languages:
Languages, like genes, evolve by a process of descent with modification. This striking similarity between biological and linguistic evolution allows us to apply phylogenetic methods to explore how languages, as well as the people who speak them, are related to one another through evolutionary history. Language phylogenies constructed with lexical data have so far revealed population expansions of Austronesian, Indo-European and Bantu speakers. However, how robustly a phylogenetic approach can chart the history of language evolution and what language phylogenies reveal about human prehistory must be investigated more thoroughly on a global scale. Here we report a phylogeny of 59 Japonic languages and dialects. We used this phylogeny to estimate time depth of its root and compared it with the time suggested by an agricultural expansion scenario for Japanese origin. In agreement with the scenario, our results indicate that Japonic languages descended from a common ancestor approximately 2182 years ago. Together with archaeological and biological evidence, our results suggest that the first farmers ...
April 19, 2011
The Pith: Over the past 10,000 years a small coterie of farming populations expanded rapidly and replaced hunter-gatherer groups which were once dominant across the landscape. So, the vast majority of the ancestry of modern Europeans can be traced back to farming cultures of the eastern Mediterranean which swept over the west of Eurasia between 10 and 5 thousand years before the before.
Dienekes Pontikos points me to a new paper in PNAS which uses a coalescent model of 400+ mitochondrial DNA lineages to infer the pattern of expansions of populations over the past ~40,000 years. Remember that mtDNA is passed just through the maternal lineage. That means it is not subject to the confounding dynamic of recombination, allowing for easier modeling as a phylogenetic tree. Unlike the autosomal genome there’s no reticulation. Additionally, mtDNA tends to be highly mutable, and many regions have been presumed to be selectively neutral. So they are the perfect molecular clock. There straightforward drawback is that the history of one’s foremothers may not be a good representative of the history of one’s ...
December 11, 2010
After linking to Marnie Dunsmore’s blog on the Neolithic expansion, and reading Peter Bellwood’s First Farmers, I’ve been thinking a bit on how we might integrate some models of the rise and spread of agriculture with the new genomic findings. Bellwood’s thesis basically seems to be that the contemporary world pattern of expansive macro-language families (e.g., Indo-European, Sino-Tibetan, Afro-Asiatic, etc.) are shadows of the rapid demographic expansions in prehistory of farmers. In particular, hoe-farmers rapidly pushing into virgin lands. First Farmers was published in 2005, and so it had access mostly to mtDNA and Y chromosomal studies. Today we have a richer data set, from hundreds of thousands of markers per person, to mtDNA and Y chromosomal results from ancient DNA. I would argue that the new findings tend to reinforce the plausibility of Bellwood’s thesis somewhat.
The primary datum I want to enter into the record in this post, which was news to me, is this: the island of Cyprus seems to have been first settled (at least in anything but trivial numbers) by Neolithic populations from mainland Southwest Asia.* In fact, the first farmers in Cyprus perfectly replicated the physical culture of the nearby mainland in toto. This implies that the genetic heritage of modern Cypriots is probably attributable in the whole to expansions of farmers from Southwest Asia. With this in mind let’s look at Dienekes’ Dodecad results at K = 10 for Eurasian populations (I’ve reedited a bit):
Modern Cypriots exhibit genetic signatures which shake out into three putative ancestral groups. West Asian, which is modal in the Caucasus region. South European, modal in Sardinia. And Southwest Asian, which is modal in the Arabian peninsula. Cypriots basically look like Syrians, but with less Southwest Asian, more balance between West Asian and South European, and far less of the minor components of ancestry.
Just because an island was settled by one group of farmers, it does not mean that subsequent invasions or migrations could not have an impact. The indigenous tribes of Taiwan seem to be the original agriculturalists of that island, and after their settlement there were thousands of years of gradual and continuous cultural change in situ. But within the last 300 years settlers from Fujian on the Chinese mainland have demographically overwhelmed the native Taiwanese peoples.
During the Bronze Age it seems Cyprus was part of the Near East political and cultural system. The notional kings of Cyprus had close diplomatic relations with the pharaohs of Egypt. But between the end of the Bronze Age and the Classical Age Cyprus became part of the Greek cultural zone. Despite centuries of Latin and Ottoman rule, it has remained so, albeit with a prominent Turkish minority.
One thing notable about Cyprus, and which distinguishes it from mainland Greece, is the near total absence of a Northern European ancestral component. Therefore we can make the banal inference that Northern Europeans were not initially associated with the demographic expansions of farmers from the Middle East. Rather, I want to focus on the West Asian and Southern European ancestral components. One model for the re-population of Europe after the last Ice Age is that hunter-gatherers expanded from the peninsular “refugia” of Iberia and Italy, later being overlain by expansions of farmers from the Middle East, and perhaps Indo-Europeans from the Pontic steppe. I have a sneaking suspicion though that what we’re seeing among Mediterranean populations are several waves of expansion out of the Near East. I now would offer the tentative hypothesis that the South European ancestral element at K = 10 is a signature of the first wave of farmers which issued out of the Near East. The West Asians were a subsequent wave. I assume that the two groups must correlate to some sort of cultural or technological shift, though I have no hypothesis as to that.
From the above assertions, it is clear that I believe modern Sardinians are descendants of that first wave of farmers, unaffected by later demographic perturbations. I believe that Basques then are a people who emerge from an amalgamation of the same wave of seafaring agriculturalists with the indigenous populations preceding them (the indigenes were likely the descendants of a broad group of northern Eurasians who expanded after the end of the last Ice Age from the aforementioned refugia). They leap-frogged across fertile regions of the Mediterranean and pushed up valleys of southern France, and out of the Straits of Gibraltar. Interestingly, the Basque lack the West Asian minority element evident in Dienekes’ Spaniards, Portuguese, as well as the HGDP French (even up to K = 15 they don’t shake out as anything but a two way admixture, while the Sardinians show a minor West Asian component). Also, the West Asian and Southern European elements are several times more well represented proportionally among Scandinavians than Finns. The Southern European element is not found among the Uyghur, though the Northern European and West Asian one is. I infer from all these patterns that the Southern European element derived from pre-Indo-European farmers who pushed west from the Near East. It is the second largest component across much of the Northwestern Europe, the largest across much of Southern European, including Greece.
A second issue which First Farmers clarified are differences between the spread of agriculture from the Near East to Europe and South Asia. It seems that the spread of agriculture across South Asia was more gradual, or least had a longer pause, than in Europe. A clear West Asian transplanted culture arrived in what is today Pakistan ~9,000 years ago. But it does not seem that the Neolithic arrived to the far south of India until ~4,000 years ago. I think that a period of “incubation” in the northwest part of the subcontinent explains the putative hybridization between “Ancient North Indians” and “Ancient South Indians” described in Reconstructing Indian population history. The high proportion of “Ancestral North Indian,” on the order of ~40%, as well as Y chromosomal markers such as R1a1a, among South Indian tribal populations, is a function of the fact that these groups are themselves secondary amalgamations between shifting cultivators expanding from the Northwest along with local resident hunter-gatherer groups which were related to the ASI which the original West Asian agriculturalists encountered and assimilated in ancient Pakistan (Pathans are ~25% ASI). I believe that the Dravidian languages arrived from the Northwest to the south of India only within the last 4-5,000 with the farmers (some of whom may have reverted to facultative hunter-gathering, as is common among tribals). This relatively late arrival of Dravidian speaking groups explains why Sri Lanka has an Indo-European presence to my mind; the island was probably only lightly settled by farming Dravidian speakers, if at all, allowing Indo-European speakers from Gujarat and Sindh to leap-frog and quickly replace the native Veddas, who were hunter-gatherers.
Note: Here is K = 15.
* Wikipedia says there were hunter-gatherers, but even here the numbers were likely very small.
December 3, 2010
A new paper in The New Journal of Physics shows that a relatively simple mathematical model can explain the rate of expansion of agriculture across Europe, Anisotropic dispersion, space competition and the slowdown of the Neolithic transition:
The front speed of the Neolithic (farmer) spread in Europe decreased as it reached Northern latitudes, where the Mesolithic (hunter-gatherer) population density was higher. Here, we describe a reaction–diffusion model with (i) an anisotropic dispersion kernel depending on the Mesolithic population density gradient and (ii) a modified population growth equation. Both effects are related to the space available for the Neolithic population. The model is able to explain the slowdown of the Neolithic front as observed from archaeological data
The paper is open access, so if you want more of this:
Just click through above. Rather, I am curious more about their nice visualization of the archaeological data:
Note how much variance there is in terms of the rate of change of the clines. As I’ve observed before there was a “break out” of the LBK farmers into Central Europe nearly 7,000 years ago, but it took much longer to close the gap between the farms on the frontier and the sea. This is well known from the archaeology, as there seems to have been a pause of ~1,000 years across much of the north European plain. On the scale of 10,000 years that’s not much time, but that’s about 40 generations. In Frisia it looks like the spreading of farming stopped for nearly ~2000 years!
Why the abatement of the spread of farming? I think the authors of the above paper are correct in their acceptance of the conventional wisdom of greater Mesolithic densities in Northern Europe. But I think perhaps a better description might be maritime Northern Europe. We often imagine early farmers displacing hunters and gatherers of game and herb, but what if in much of the world the main clash numerically was between dense populations oriented toward the sea, and those who were depended on the land? About seven years ago a study came out which argued for a rapid transition from seafood to meat in the diets of early Britons, Why Did Ancient Britons Stop Eating Fish?:
When cattle, sheep, pigs, and wheat arrived on the shores of Great Britain about 5,000 years ago, fish quickly fell off the Neolithic menu, according to an analysis of human bones scattered throughout the island.
“Farming really took off in Britain during the Neolithic. The main questions concerning the speed of change relates to how quickly Mesolithic peoples adapted—or otherwise—to the new farming methods and/or the spread of farming into Britain by new farming communities,” he said.
The research by Richards and colleagues Rick Schulting at Queen’s University Belfast and Robert Hedges at the University of Oxford tracks the shift in diet by examining the dietary signature stored in the bones.
They find that the shift was rapid and complete at the onset of the Neolithic. “Marine foods, for whatever reason, seem to have been comprehensively abandoned,” the researchers conclude in the September 25 issue of the journalNature.
“We determined that after the introduction of domesticates, as well as the other artifacts associated with the Neolithic, the isotope values showed that marine foods were not used anymore,” he said. “We then infer that this is a switch from wild foods such as fish and shellfish to the new domesticates that arrive at this time.”
Richards said there are three plausible reasons why the British abandoned seafood from the beginning of the Neolithic: the domesticated plants and animals presented a steady source of food; the shift was forced by a climate change; or cultural pressure.
In the early 2000s the idea of wholesale rapid demographic replacement was not in the air. I think we need to put that back on the table. Here is the chart on isotope ratios from the 2003 paper:
Notice the sharp discontinuity. Richards et al. in 2003 interpreted this as a rapid cultural acquisition of the Neolithic lifestyle ~2500-3000 BC. They note in the media reports that later Britons, for example at the time of the Roman conquest, seem to have utilized fish a bit more in their diet than these early Neolithics. This stands to reason, much of Britain is not too far from the sea. To me the very sharp drop in marine consumption is indicative more of a food taboo, than a practical shift. Obviously farmers would primarily be subsistent on grain, but there’s no necessary reason to avoid meat or fish, but as it happens in many parts of the world societies preserve and perpetuate exactly such norms. These norms may have spread through cultural diffusion, for example through an adoption of a new religion. Or, the norms may have been brought by a new group which arrived in large numbers and replaced the indigenous population.
Here is an equivalent chart from Denmark from an earlier paper by the same group:
When we think of peoples who aren’t farmers, we often think of marginalized nomadic or semi-nomadic groups. Many of the remaining hunter-gatherers such as Bushmen, as well societies which supplement their conventional lifestyle with a lot of hunting & gathering, such as the indigenous peoples of Siberia or the Sami of northern Scandinavia, occupy territory which is simply not viable for conventional agriculture. But this was not so in the past. Before the farmers arrived the rich bottom-lands were occupied by hunters & gatherers, of fish, game, grain, and nuts. In certain ecologies, such as around productive estuaries one could imagine enormous aggregations of these peoples. Additionally, it seems likely that a sedentary lifestyle predates farming. A good contemporary analog for what ancient Northern Europe may have been like was the Pacific Northwest before the European settlement. These native tribes were relatively affluent because of the abundance of salmon runs, and engaged in lavish signalling, such as with their famous potlatches. Seeing as how there are Atlantic salmon runs in places like Norway and Scotland one can make even closer correspondences perhaps!
As I have stated before just because we have no written records of this period, we can not assume that these were necessarily the fragmented and scattered “small-scale societies” which we’re familiar with today. There may have been ideologically motivated political coalitions and alliances which broke down along ethnic and cultural lines. In the paper above the authors argue that there is evidence that a climatic constraint, crops which do not have a good yield in cooler or warmer temperatures, is a weak hypothesis. If so I wonder if it is a bit too pat to simply model the dynamics as a diffusive “bottom up” process. Seems plausible enough for much of Europe where Mesolithic populations were thin on the ground because of local carrying capacity, but I suspect that the encounter between dense agglomerations of farmers and fishermen resulted in an inevitable ramp up of political integration and consolidation, as villages and tribes had to coordinate together because of a positive feedback loop of conflict.
Image Credit: Lordkinbote, Mactographer